Great Smoky Mountains National Park

Visitation to the national park is consistently above 10 million people per annum, with a new record of over 12.5 million set in 2019 (NPS, 2020b). This contributes to localized on-the-ground impacts, primarily in high-use areas (NPS, 2016) and the park has noted in the past that "congestion inside and outside of the park detracts from scenic beauty" (NPS, 2016). The park reports an increase in vandalism and graffiti on tunnels, walls, and boulders (NPS, 2016). As of 2016, budgets and staffing had not increased to match increases in visitation and maintenance costs (NPS, 2016) and in 2018, the park had over $235 million in deferred maintenance of infrastructure (NPS, 2018). However, in June 2020, the U.S. Congress passed the Great American Outdoors Act, which "establishes the National Parks and Public Land Legacy Restoration Fund to support deferred maintenance projects on federal lands" (U.S. Congress, 2020). This fund will provide "$9.5 billion over five years to address priority repairs in national parks and other public lands" (SELC, 2020), and $6.65 billion of this fund will be directed to national parks to address critical repairs (Pew, 2020). This legislation also makes permanent the Land and Water Conservation Fund. Closure of the park due to COVID-19 on 24 March 2020 (NPS, 2020q) will significantly reduce both numbers and impacts in the current year. It is not known what the long-term effect of this measure will be, however park staff are monitoring air quality during closure from the COVID-19 pandemic, to see if a reduction in emissions inside the park has any effects on air quality in the park (WBIR, 2020).

Air pollutants from sources outside the park, though reduced from levels in decades past due to emission controls, are having a wide range of documented impacts, tarnishing scenic views, increasing the pH in high-elevation streams, depositing mercury, and damaging plants (NPS, 2016). Although 5 park water resources are designated as “Outstanding Natural Resource Waters”, 12 of the park's streams are listed by the EPA as impaired due to acidification, and some 18% of park streams are currently too acidic to support fish and other aquatic life; this source says that some models indicate that it will take over 100 years for some streams to recover sufficiently to support fish again. Airborne pollution from nearby agriculture in the region contributes to the park’s nitrogen deposition (NPS, 2016). However, as of 2017, several air pollution metrics show an improving trend over the previous 10 years: visibility/haze index is fair and improving; ozone/vegetation health is fair and improving; sulfur deposition/wet deposition is poor but improving (NPS, 2017a). Nitrogen deposition/wet deposition is poor with an unchanging trend, but the park’s ecosystems have very low sensitivity to nitrogen-enrichment effects (NPS, 2017a). According to the park, “mercury deposition is increasingly posing a significant threat to the food web of aquatic and terrestrial resources of the park” (NPS, 2016).

According to park literature, the national park is facing one of its greatest eclogical crises since the chestnut blight in the form of the hemlock woolly adelgid (NPS and GSMA, 2010). Forest health is declining, affecting key species (NPS, 2016). Without successful intervention, the invasive hemlock woolly adelgid is likely to kill most of the hemlocks, which play an important role by providing deep shade along creeks, maintaining cool micro-climates critical to survival of trout and other cold-water species. The impact of widespread loss of hemlock could trigger changes more significant than those that followed the demise of the American Chestnut in the 1930s and 40s (NPS, 2020c). The introduced balsam woolly adelgid (Adelges piceae) is an insect pest that infests and kills stands of Fraser fir (Abies fraseri), formerly the dominant tree at the highest elevations; affected trees literally starve to death, and thousands of dead trees are all that are left on the highest mountain peaks (NPS, 2020c). Further serious impacts to the vegetation and ecosystems of the park are occurring from the Emerald Ash Borer and the Dogwood Anthracnose (NPS, 2020; NPS data.gov, 2020; Kays, 2017). There are over 380 non-native plant species in the park; 35 of those are aggressive and pose a threat to the park’s ecosystems. Many of these species are found in sites that have undergone recent disturbance, and, once established, they are aggressive competitors with native plants and can change natural succession. Other problems caused by non-native plants include interbreeding with closely related native species and out-competing rare native plants that require specialized  habitats. At least 8 of these species are prolific in the park (Japanese grass, privet, multiflora rose, Japanese honeysuckle, mimosa garlic mustard, oriental bittersweet, musk thistle), and present a significant threat to the ecosystem (NPS, 2004, 2016, 2020c). Exotic wild hogs in the park damage wetlands and other habitats, compete with native animals for food, and introduce diseases. According to the NPS, 'the hogs will eat just about anything, including red-cheeked salamanders (Plethodon jordani), which are found only in the park, and the roots and foliage of wildflowers that often take years to mature and bloom'; a combination of trapping, shooting and establishment of exclosures is used by the NPS to manage this problem (NPS, 2020c). Introduced rainbow and brown trout are competing with native Brook Trout (Moore et al., 2005). According to sources, the native brook trout have lost 75% of their range within the park since the 1900s (NPS, 2020a).  Collectively, virtually all of the park's ecosystems are under threat from the particular and cumulative impacts of this huge range of exotic plants, animals, insects and pathogens.

The little brown bat faces a serious threat of extinction from the white-nose syndrome (NPS, 2020d). While assessed  as 'low threat' to the Outstanding Universal Value of the World Heritage site, it is an existential threat to this species and contributes to cumulative impacts on the site.

According to the park sources, “noise and light pollution are affecting the wilderness experience in some areas” (NPS, 2016). In particular, “the sound of motorcycle traffic on the park roads can be heard a considerable distance into the wilderness”, and “low-level overflights by air-tour helicopters have been a persistent issue for a number of years” (NPS, 2016). The park is currently working with the Federal Aviation Administration to implement the National Parks Air Tour Management Act of 2000 (amended in 2012) (FAA, 2020). In 2019, a schedule was announced for the park to develop Voluntary Agreements with air tour operators (as allowed under the 2012 amendment), to be finalized in 2022 (NPS 2019). The impacts of light pollution from increasing residential and commercial development (outside the park) on the clarity of the park's night skies have been noted (NPS, 2016).

The park's historic and prehistoric fire regime was altered by decades of deliberate fire suppression and fire prevention in the 20th century. In the last 25 years, there has been a substantial change of policy, resulting in significant parts of the park treated with prescribed burns (NPS, 2020g). The NPS has made considerable positive progress on this front.